The company will fan out 36 onshore field teams and 13 offshore vessels for exploration with an investment of Rs 3,500 crore (Rs 35 billion).

Subir Raha, chairman and managing director, said the effort was to maintain positive reserve accretion rate for five consecutive years.

"Since 2001, we have managed to add 210 million tonne recoverable component in our kitty while the production has been 200 million tonne. Late 90s had seen some decline in addition but the trend has reversed," Raha said in Kolkata on Tuesday.

ONGC has set the target to discover 6 billion tonne oil and gas equivalent which can give 2 billion tonne of recoverable reserve.

Of the in-place reserve, four billion tonne will come from deepwater blocks and two billion from onshore and frontier basins.

Y B Sinha, director (exploration) of ONGC, said seismic data (2D/3D and 4D) would be acquired and processed by number of computing centres in Mumbai, Kolkata, Baroda, Chennai apart from Dehradun. Following this, the data would be interpreted by internal specialists of the company.

ONGC has one survey vessel, which has an on-board data processing capability. The rest 12 ships would be chartered for the survey work. The chartering cost alone would come about $ 200 million.

"This is a very important stage of the exploration phase. Based on the date acquired, processed and interpreted, we will go for drilling in respective fields," Raha pointed out. ONGC has one of the most sophisticated computing system in the country.

The exercise will not only cover new areas where exploration is at its early phase but also all 115 producing fields to increase output further.

ONGC employees struggle through adverse condition both physical and security wise, to carry out the survey.

The chairman said company was betting big on the Sagar Samridhhi, the deepwater drilling project.

"We went ahead with this venture, biggest of its kind by a single operator in the world. We invited 17 international majors to work with us, but nobody responded favourably," he informed.